An interface circuit as mentioned in the opening paragraph is described in US2010/0033095 A1.
Fluorescent lamps are highly efficient light sources that have been in use for many years. The efficiency and lifetime of fluorescent lamps are particularly high when they are driven by an electronic lamp driver that supplies a high frequency lamp current with a frequency in the order of 10 kHz. As a consequence, luminaires comprising such a high frequency fluorescent lamp driver are present in homes and offices all over the world. However, in recent years alternative electrically powered light sources in the form of LEDs and OLEDs or high pressure discharge lamps have become available that have an efficiency and a lifetime that is even higher than that of a fluorescent lamp. Consequently, it is desirable to replace the fluorescent lamp in the existing luminaires by a light source based on LEDs or OLEDs or by a high pressure discharge lamp in order to increase the efficiency and/or the lifetime of the light source in use. Since LEDs and OLEDs need to be operated with a DC-current instead of a high frequency AC-current, it is not possible to simply replace the fluorescent lamp by a LED array. Also in the case of a high pressure discharge lamp it is preferred to supply the light source with a DC-current, possibly commutated at a low frequency. It is thus necessary to make use of an interface circuit connected between the lamp terminals of the high frequency fluorescent lamp driver and the light source that replaces the fluorescent lamp. The interface circuit and the light source together must emulate a fluorescent lamp, when the interface circuit and the light source are jointly connected to the lamp connection terminals and the high frequency fluorescent lamp driver goes through the lamp operating stages: preheat, ignition and stationary operation. Furthermore, the interface circuit must convert the high frequency AC voltage supplied by the high frequency lamp driver into a DC-current that supplies the light source.